The advantage of a fastener driving apparatus actuated by means of a propulsive charge, comprising powder, is that it is independent and may provide variable driving power of energy.
In order to achieve this objective charges of different powders are often used.
In indirect firing fastener driving apparatus, the power transmitted to the piston may also be varied by varying the volume of the combustion chamber.
An apparatus of the above mentioned type is already known by means of the document FR-A-2 329 415. The apparatus of this document however has some drawbacks. Power adjustment is achieved by means of rotation of the breech. The piston is positioned within the barrel, as a function of the desired power, during abutment of the apparatus so as to place it in the firing position. Such an operation results in a supplemental effort which increases the abutment effort.
Document US-A-3,652,003 also teaches an apparatus of the same type, however, the same also has some drawbacks. Its adjustment means is mounted upon the barrel-holder and is intended to cooperate with a stop fixed upon and projecting out from the barrel. Upon firing with respect to particular materials, the piston may rebound and be driven into the bottom of the barrel. In this case, the adjustment means no longer has any effect upon the position of the piston within the barrel. Upon opening the apparatus, the pawl no longer acts upon the iston, or the relative position of the pawl and the adjustment means is no longer taken into account, and the piston remains at the position of maximum power even though the adjustment means may be at a position of intermediate power. A correct positioning as a function of the desired power cannot therefore always be assured by means of this apparatus.
An apparatus of the above mentioned type is additionally known from the document FR-A-2 218 168. However, it relates to an apparatus with a complex adjustment means. Positioning of the piston is effected upon closing the apparatus, the adjustment means is acted upon by opening the apparatus and closing it, and in addition, such operation also causes the abutment effort to be increased. This adjustment means also comprises a spring which may cause variations of the power adjustment.